Update

I checked out an old project of mine and noticed that it was already centered. It turns out that CommonMark allows you to set align="center" on <div> tags as well!

So, the simplest solution for centering is currently (note the empty line after the opening <div>:

<div align="center">

# This is gonna be centered!
</div>

Original

The only CommonMark html object that supports centering (as far as I know) is when you center a table cell. First you might've thought about just making a table and then using align="center", but the table won't take up the entire width of the page, so you'd get a small table on the left hand side of the page, which wouldn't solve our problem of wanting to center stuff relative to the page rather than the table.

To get around this we set the table width (not using CSS with an inline style tag since it's not supported in CommonMark at the time of writing) to a large value that will take up way more than the total width of the page. Since the max-width: CSS property of tables in Gitlab markdown is 100% it means that by setting a ridiculously high width="" we're essentially setting the table width: to 100% by using only the allowed pure html width="" property.

The markdown below if placed in e.g. README.md in your Gitlab project will result in a 100% width table with a centered image, title and description. The most notable part is that we're setting width="9999" on the <td> element in the table.

<table align="center"><tr><td align="center" width="9999">
<img src="/icon.png" align="center" width="150" alt="Project icon">

# MyProject

Description for my awesome project
</td></tr></table>

... More content

Below you can see an example of how your README.md file could look on Gitlab using the above markdown.